Provided by: nco_4.5.4-1build1_amd64 
NAME
ncatted - netCDF Attribute Editor
SYNTAX
ncatted [-a att_dsc] [-a ...] [--bfr sz][-D dbg_lvl] [--glb att_name= att_val]] [-h] [--hdr_pad sz] [-l
path] [-O] [-p path] [-R] [-r] [--ram_all] input-file [ output-file]
DESCRIPTION
ncatted edits attributes in a netCDF file. If you are editing attributes then you are spending too much
time in the world of metadata, and ncatted was written to get you back out as quickly and painlessly as
possible. ncatted can append, create, delete, modify, and overwrite attributes (all explained below).
Furthermore, ncatted allows each editing operation to be applied to every variable in a file, thus saving
you time when you want to change attribute conventions throughout a file. ncatted interprets character
attributes as strings.
Because repeated use of ncatted can considerably increase the size of the history global attribute, the
-h switch is provided to override automatically appending the command to the history global attribute in
the output-file.
When ncatted is used to change the _FillValue attribute, it changes the associated missing data self-
consistently. If the internal floating point representation of a missing value, e.g., 1.0e36, differs
between two machines then netCDF files produced on those machines will have incompatible missing values.
This allows ncatted to change the missing values in files from different machines to a single value so
that the files may then be concatenated together, e.g., by ncrcat, without losing any information.
The key to mastering ncatted is understanding the meaning of the structure describing the attribute
modification, att_dsc. Each att_dsc contains five elements, which makes using ncatted somewhat
complicated, but powerful. The att_dsc argument structure contains five arguments in the following
order:
att_dsc = att_nm, var_nm, mode, att_type, att_val
att_nm Attribute name. Example: units
var_nm Variable name. Example: pressure
mode Edit mode abbreviation. Example: a. See below for complete listing of valid values of mode.
att_type
Attribute type abbreviation. Example: c. See below for complete listing of valid values of
att_type.
att_val
Attribute value. Example: pascal. There should be no empty space between these five consecutive
arguments. The description of these arguments follows in their order of appearance.
The value of att_nm is the name of the attribute you want to edit. This meaning of this should be clear
to all users of the ncatted operator.
The value of var_nm is the name of the variable containing the attribute (named att_nm) that you want to
edit. There are two very important and useful exceptions to this rule. The value of var_nm can also be
used to direct ncatted to edit global attributes, or to repeat the editing operation for every variable
in a file. A value of var_nm of global” indicates that att_nm refers to a global attribute, rather than
a particular variable's attribute. This is the method ncatted supports for editing global attributes.
If var_nm is left blank, on the other hand, then ncatted attempts to perform the editing operation on
every variable in the file. This option may be convenient to use if you decide to change the conventions
you use for describing the data.
The value of mode is a single character abbreviation ( a, c, d, m, or o) standing for one of five editing
modes:
a Append. Append value att_val to current var_nm attribute att_nm value att_val, if any. If var_nm
does not have an attribute att_nm, there is no effect.
c Create. Create variable var_nm attribute att_nm with att_val if att_nm does not yet exist. If
var_nm already has an attribute att_nm, there is no effect.
d Delete. Delete current var_nm attribute att_nm. If var_nm does not have an attribute att_nm,
there is no effect. When Delete mode is selected, the att_type and att_val arguments are
superfluous and may be left blank.
m Modify. Change value of current var_nm attribute att_nm to value att_val. If var_nm does not
have an attribute att_nm, there is no effect.
o Overwrite. Write attribute att_nm with value att_val to variable var_nm, overwriting existing
attribute att_nm, if any. This is the default mode.
The value of att_type is a single character abbreviation ( f, d, l, s, c, or b) standing for one of the
six primitive netCDF data types:
f Float. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_FLOAT.
d Double. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_DOUBLE.
l Long. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_LONG.
s Short. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_SHORT.
c Char. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_CHAR.
b Byte. Value(s) specified in att_val will be stored as netCDF intrinsic type NC_BYTE. The
specification of att_type is optional in Delete mode.
The value of att_val is what you want to change attribute att_nm to contain. The specification of
att_val is optional in Delete mode. Attribute values for all types besides NC_CHAR must have an
attribute length of at least one. Thus att_val may be a single value or one-dimensional array of
elements of type att_type. If the att_val is not set or is set to empty space, and the att_type is
NC_CHAR, e.g., -a units,T,o,c,"" or -a units,T,o,c,, then the corresponding attribute is set to have zero
length. When specifying an array of values, it is safest to enclose att_val in double or single quotes,
e.g., -a levels,T,o,s,"1,2,3,4" or -a levels,T,o,s,'1,2,3,4'. The quotes are strictly unnecessary around
att_val except when att_val contains characters which would confuse the calling shell, such as spaces,
commas, and wildcard characters.
NCO processing of NC_CHAR attributes is a bit like Perl in that it attempts to do what you want by
default (but this sometimes causes unexpected results if you want unusual data storage). If the att_type
is NC_CHAR then the argument is interpreted as a string and it may contain C-language escape sequences,
which NCO will interpret before writing anything to disk. NCO translates valid escape sequences and
stores the appropriate ASCII code instead. Since two byte escape sequences represent one byte ASCII
codes, e.g., ASCII 10 (decimal), the stored string attribute is one byte shorter than the input string
length for each embedded escape sequence. These sequences in particular allow convenient editing of
formatted text attributes. See ncks netCDF Kitchen Sink, for more examples of string formatting (with
the ncks -s option) with special characters.
Analogous to printf, other special characters are also allowed by ncatted if they are "protected" by a
backslash. NCO simply strips away the leading backslash from these characters before editing the
attribute. No other characters require protection by a backslash. Backslashes which precede any other
character will not be filtered and will be included in the attribute.
Note that the NUL character which terminates C language strings is assumed and need not be explicitly
specified. If NUL is input, it will not be translated (because it would terminate the string in an
additional location). Because of these context-sensitive rules, if wish to use an attribute of type
NC_CHAR to store data, rather than text strings, you should use ncatted with care.
EXAMPLES
Append the string "Data version 2.0.\n" to the global attribute history:
ncatted -O -a history,global,a,c,"Data version 2.0\n" in.nc
Note the use of embedded C language printf()-style escape sequences.
Change the value of the long_name attribute for variable T from whatever it currently is to
"temperature":
ncatted -O -a long_name,T,o,c,temperature in.nc
Delete all existing units attributes:
ncatted -O -a units,,d,, in.nc
The value of var_nm was left blank in order to select all variables in the file. The values of att_type
and att_val were left blank because they are superfluous in Delete mode.
Modify all existing units attributes to "meter second-1"
ncatted -O -a units,,m,c,"meter second-1" in.nc
Overwrite the quanta attribute of variable energy to an array of four integers.
ncatted -O -a quanta,energy,o,s,"010,101,111,121" in.nc
See the manual for more complex examples, including how to input C-language escape sequences and other
special characters like backslashes and question marks.
AUTHOR
NCO manual pages written by Charlie Zender and originally formatted by Brian Mays.
REPORTING BUGS
Report bugs to <http://sf.net/bugs/?group_id=3331>.
COPYRIGHT
Copyright © 1995-2016 Charlie Zender
This is free software; see the source for copying conditions. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The full documentation for NCO is maintained as a Texinfo manual called the NCO User's Guide. Because
NCO is mathematical in nature, the documentation includes TeX-intensive portions not viewable on
character-based displays. Hence the only complete and authoritative versions of the NCO User's Guide are
the PDF (recommended), DVI, and Postscript versions at <http://nco.sf.net/nco.pdf>,
<http://nco.sf.net/nco.dvi>, and <http://nco.sf.net/nco.ps>, respectively. HTML and XML versions are
available at <http://nco.sf.net/nco.html> and <http://nco.sf.net/nco.xml>, respectively.
If the info and NCO programs are properly installed at your site, the command
info nco
should give you access to the complete manual, except for the TeX-intensive portions.
ncap(1), ncap2(1), ncatted(1), ncbo(1), nces(1), ncecat(1), ncflint(1), ncks(1), nco(1), ncpdq(1),
ncra(1), ncrcat(1), ncremap(1), ncrename(1), ncwa(1)
HOMEPAGE
The NCO homepage at <http://nco.sf.net> contains more information.
NCATTED(1)